Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Carnot

Bell Coleman

2. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

3. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

4. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

5. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

Water will never evaporate

6. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

1: 1

9: 1

7. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

8. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

9. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

10. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

Toxic

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

12. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

13. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

14. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

15. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

16. Most thermostatic expansion valves are set for a superheat of

5°C

10°C

15°C

20°C

17. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

18. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

Condenser and receiver

19. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

20. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

1.33

2.33

Page 3 of 4

21. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Always more than unity

Any one of the above

22. The capillary tube, as an expansion device, is used in

Water coolers

All of these

Room air conditioners

Domestic refrigerators

23. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

15 bar

8 bar

2 bar

24. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

25. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

26. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

27. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

28. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Piston type reciprocating

Axial

29. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Carnot

Reversed Carnot

30. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

Any value

High

Page 4 of 4

31. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

32. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

33. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

34. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

35. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

36. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

37. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Ammonia

Carbon dioxide

Brine

38. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.4

0.6

39. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

40. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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